Fifteen Italian police officers and doctors were last night sentenced to jail terms of up to five years after being found guilty of abusing protesters detained during riots at the 2001 G8 summit in Genoa.

Thirty other defendants were cleared of charges ranging from assault to the denial of basic human rights. The judges issued their verdicts after 11 hours of closed-doors deliberations.

The sentences totalled less than a third of what had been demanded by the prosecution. But they will nevertheless be embarrassing for Silvio Berlusconi and his rightwing allies, in office in Italy both then and now.

The court heard former detainees including Britons testify that they were insulted, beaten and sprayed with asphyxiating gas. Some were threatened with rape.

Detainees were made to join in chants in praise of Italy's late fascist dictator, Benito Mussolini. Another chant, lauding Chile's Augusto Pinochet, ended: "Death to the Jews."

Between 100,000 and 200,000 demonstrators converged on Genoa seven years ago to take part in anti-globalisation protests. Most were peaceable, but some were not, and the situation deteriorated as the police employed tactics that many witnesses described as heavy-handed.

The violence peaked with the death of a 23-year-old Italian demonstrator, shot dead by a conscript Carabiniere. More than 250 of those arrested were taken to a holding camp that had been created at Bolzaneto, six miles from Genoa, where the abuses took place.

The heaviest sentence, five years, was given to the camp commander, Antonio Biagio Gugliotta. Twelve other police officers, eight men and four women, received jail terms of five to 28 months.

The chief of medical services at Bolzaneto, Giacomo Toccafondi, was given one year and two months in jail; he was accused of insulting detainees and failing to inform authorities after they were sprayed with asphyxiating gas in cells.

The detainees at Bolzaneto included about 40 who were arrested in a raid on a school being used as a dormitory. A judge ruled that there was no evidence to show any of those demonstrators had been involved in the violence in Genoa.

One, a Briton, Richard Moth, later told the Guardian that, despite injuries sustained in the raid that had him "screaming with pain", he was made to stand for hours spread-eagled against a wall.

The Bolzaneto trial was one of three arising from the Genoa G8 summit. In December 2007, 24 demonstrators were found guilty of damage to property and looting. They were given sentences ranging from five months to 11 years. In the third, ongoing trial, 28 defendants, including some of Italy's most senior police officers, face charges related to the raid on the school, which left 62 injured, three in comas.